The Homogalacturonan Deconstruction System of Paenibacillus amylolyticus 27C64 Requires No Extracellular Pectin Methylesterase and Has Significant Industrial Potential

Microbial cell factories using Paenibacillus: status and perspectives

Considered a "Generally Recognized As Safe" (GRAS) bacterium, the plant growth-promoting rhizobacterium Paenibacillus has been widely applied in: agriculture, medicine, industry, and environmental remediation. Paenibacillus species not only accelerate plant growth and degrade toxic substances in wastewater and soil but also produce industrially-relevant enzymes and antimicrobial peptides. Due to a lack of genetic manipulation tools and methods, exploitation of the bioresources of naturally isolated Paenibacillus species has long been limited. Genetic manipulation tools and methods continue to improve in Paenibacillus, such as shuttle plasmids, promoters, and genetic tools of CRISPR. Furthermore, genetic transformation systems develop gradually, including: penicillin-mediated transformation, electroporation, and magnesium amino acid-mediated transformation. As genetic manipulation methods of homologous recombination and CRISPR-mediated editing system have developed gradually, Paenibacillus has come to be regarded as a promising microbial chassis for biomanufacturing, expanding its application scope, such as: industrial enzymes, bioremediation and bioadsorption, surfactants, and antibacterial agents. In this review, we describe the applications of Paenibacillus bioproducts, and then discuss recent advances and future challenges in the development of genetic manipulation systems in this genus. This work highlights the potential of Paenibacillus as a new microbial chassis for mining bioresources.

Synergistic pectin deconstruction is a prerequisite for mutualistic interactions between honeybee gut bacteria

The honeybee gut microbiome is crucial for degrading diverse pollen glycans. Yet it is unclear how this process shapes the interactions among bacteria. Here, we demonstrate a conditional mutualistic interaction between strains of two honeybee gut bacteria Bifidobacterium asteroides and Gilliamella apicola. When co-occurring in vitro and in vivo, Bifidobacterium provides complementary demethylation service to promote Gilliamella growth on methylated homogalacturonan, an enriched polysaccharide of pectin. In exchange, Gilliamella shares digestive products with Bifidobacterium, through which a positive interaction is established. This positive interaction vanishes when Bifidobacterium is not required on a non-methylated diet. Results from biochemical and gene expression analyses combined with model simulation further suggest that the ratio change of the two major homogalacturonan breakdown products, galacturonic acid (GalA) and di-GalA, determines the bacterial interaction. This study unravels how glycan metabolism may shape the interactions between honeybee gut bacteria.

Biochemical Characterization of a Pectate Lyase AnPL9 from Aspergillus nidulans

Pectinolytic enzymes have diverse industrial applications. Among these, pectate lyases act on the internal α-1,4-linkage of the pectate backbone, playing a critical role in pectin degradation. While most pectate lyases characterized thus far are of bacterial origin, fungi can also be excellent sources of pectinolytic enzymes. In this study, we performed biochemical characterization of the pectate lyase AnPL9 belonging to the polysaccharide lyase family 9 (PL9) from the filamentous fungus Aspergillus nidulans. Recombinant AnPL9 was produced using a Pichia pastoris expression system and purified. AnPL9 exhibited high activity on homogalacturonan (HG), pectin from citrus peel, pectin from apple, and the HG region in rhamnogalacturonan-I. Although digalacturonic acid and trigalacturonic acid were not degraded by AnPL9, tetragalacturonic acid was converted to 4,5-unsaturated digalacturonic acid and digalacturonic acid. These results indicate that AnPL9 degrades HG oligosaccharides with a degree of polymerization > 4. Furthermore, AnPL9 was stable within a neutral-to-alkaline pH range (pH 6.0-11.0). Our findings suggest that AnPL9 is a candidate pectate lyase for biotechnological applications in the food, paper, and textile industries. This is the first report on a fungal pectate lyase belonging to the PL9 family.